There is provided a ring opening process using a catalyst comprising a hydrogenation/dehydrogenation component, such as a noble metal, and an acidic solid component comprising a Group IVB metal oxide modified with an oxyanion of a Group VIB metal. This catalyst is used to convert cyclic hydrocarbons, such as cyclohexane and benzene, to paraffins, especially branched paraffins.
Processes and catalysts which promote the conversion of cyclic hydrocarbons to paraffins, i.e., ring opening, are important in the petroleum refining industry. A substantial portion of naturally occurring and synthetically prepared hydrocarbon fractions are naphthenic, i.e., contain significant amounts of cyclic compounds.
Since aromatics have high octane numbers, the presence of aromatics, such as benzene, or cyclics readily convertable to aromatics, such as cyclohexane, have been desirable in gasolines or reformer feeds. However, environmental concerns could require reduction in the amount of both benzene and total aromatics allowed in gasoline composition. Ring opening of cyclic hydrocarbons to yield highly branched paraffins offers a very attractive route for reducing aromatics in gasoline with minimum loss of octane and gasoline yield. Accordingly, ring opening reactions may be applied to hydrocarbon fractions boiling in the range of gasolines.
Ring opening reactions may also be applied to other fractions. For example, the presence of aromatics and/or naphthenes may not be desirable in jet fuels and high viscosity lubricating oils. Other ring opening applications include selective conversion of methylcyclopentane in hydrocarbon streams which are to be reformed to aromatics since with certain catalysts, e.g., chromia-alumina, methylcyclopentane is a catalyst poison.
A number of catalysts, e.g., platinum metal and chloride on alumina, are known to the art as useful for ring opening. In U.S. Pat. No. 3,617,511 there is described a catalyst comprising rhodium or ruthenium supported on a suitable acid-acting refractory oxide and the use of this catalyst for ring opening.
U.S. Pat. Nos. 4,783,575 and 4,834,866 disclose the use of a chlorided platinum-alumina catalyst to open hydrocarbon rings and isomerize C.sub.6 paraffins to more highly branched paraffins. However, the single pass conversion of C.sub.6 cyclics obtained over this catalyst is limited. The conversion could be increased by increasing operating conditions severity, but the C.sub.5 + yield and paraffin isomerization selectivity decrease. Furthermore, the chlorided alumina-based catalyst is troublesome to operate and handle.
U.S. Pat. No. 3,631,117 describes a process for the hydroisomerization of cyclic hydrocarbons that uses a zeolite supported Group VII metal as a catalyst for ring opening and paraffin isomerization.